The utility industry is continuously searching for efficient equipment to generate, transmit and manage electrical power.
A known system for electrical power production comprises an electricity generating source that is connected to a load. The power source is often a steam generating, coal fired or nuclear power plant. The steam is used to turn a turbine generator and the electricity produced is typically transmitted to a load via electrical transmission lines.
Since the source of energy that produces electricity is often remotely located, for example, fire burning coal, nuclear plants, etc., from the demand, for example, cities and factories, the electrical transmission lines can be hundreds of miles long. Generally, the longer the transmission lines, the greater the energy losses incurred during transmission. These losses are partly due to the resistive and reactive properties of electrical transmission lines, commonly referred to as the electric transmission line impedance. In an attempt to increase transmission efficiency, utilities often attempt to match the phase angle of the voltage at the generating end with the reactance of the load. In addition, utilities must be prepared to handle electric transmission phase angle and voltage swings. These problems are often addressed by using static VAR compensators, capacitive banks, excitation equipment or synchronized generators. These devices, however, increase costs and limit the flexibility of the system by inhibiting the ability to adapt the system to various contingencies encountered during electrical transmission.
Many of the transmission losses can be alleviated by locating the electricity generating station closer to the loads. However, since loads are usually located in areas with restrictions on pollution outputs, commonly referred to as non-attainment areas, many generating stations are prohibited by law at load areas. Furthermore, the greater the distance between the energy source, for example, coal, and the generating station, the greater the decrease in the power system's efficiency due to transportation and storage costs.
Another problem associated with power systems is the ability to store energy. The demand for electricity varies each hour of the day, depending on the needs of the consumers. Demand is usually greatest during working hours with large declines in demand during the night. Power generating systems which cannot store energy must be ramped up and down in accordance with demand. This may require the addition of stand-by gas turbine plants or the purchase of energy from other utilities. Further, the need to continuously adjust the power system to the changing load requirements raises costs by increasing the electronics, mechanics and manpower necessary to run the system. In addition, this increased complexity decreases the system's reliability.
Most utility systems can generate energy at very low cost during off-peak periods. A more efficient method of producing energy would be to run a plant at a constant rate for most of the day with the energy generated during off-peak hours stored for use during other hours. This is true even if a gas turbine system is used for peak-hour production.
Utility companies have attempted several techniques at storing energy. The pumped-hydro storage method pumps water to an uphill storage facility during off-peak hours and then uses the water to produce electricity during peak hours. The pumped-hydro storage method, however, requires large amounts of land and is expensive to construct.
Another method of storing energy comprises a compressed air energy storage system, also called the air storage system energy transfer. Using this method, utilities have pumped air into large underground caverns during off-peak hours and then used the compressed air to generate energy during peak hours. The compressed air energy storage system, however, requires the plant to be located near a suitable air storage cavern.
As an alternative to storing the air in underground caverns, some utilities have attempted to store the air in manufactured tanks or tubes. These attempts have generally failed since the volume of storage required has been prohibitive.
In addition to the geographic limitations of the pumped-hydro storage system and the compressed air energy system, neither system addresses the transmission line problem. In fact, since both systems must be located near a suitable geographic location, it is likely that the electrical transmission lines used to transfer the energy will be longer and less efficient. Further, strict regulations now make it difficult to construct electrical transmission lines in many areas.